1. Field of the Invention
The present invention generally relates to a direct type backlight module with point light sources, the direct type backlight module typically being used in a liquid crystal display (LCD) device.
2. Discussion of the Related Art
Most liquid crystal display (LCD) devices are passive devices in which images are displayed by controlling an amount of light input from an outside light source. Thus, a separate artificial light source (for example, a backlight module) is generally employed for irradiating an LCD panel that has the LCD device.
Generally, backlight modules are classified as edge type or direct type, based upon the arrangement of one or more lamps thereof. The edge type backlight module has a lamp arranged at a side portion of a light guiding plate that is used for guiding light. The edge type backlight module is commonly employed in small-sized LCDs because it is lightweight, small, and has low power consumption. However, the edge type backlight module is generally not suitable for large-sized LCDs (20 inches or more). A direct type backlight module usually has a plurality of lamps arranged in a regular array. The lamps directly illuminate an entire major surface of a light guiding plate. The light passes directly through the light guiding plate to illuminate an LCD panel. Direct type backlight modules have a higher efficiency of utilization of light energy and a longer operational service life than edge type backlight modules, and are commonly produced for large-sized LCDs.
The lamps of the direct type backlight module can be selected from the group consisting of cold cathode fluorescent lamps (CCFLs) and light emitting diodes (LEDs). LEDs provide a purer color, have a lower operation voltage, and are lighter compared to CCFLs. Thus LEDs are more commonly used in direct type backlight modules.
Referring to FIG. 10, a typical direct type backlight module is shown. The backlight module includes a housing 210, a plurality of LEDs 220 acting as light sources, a reflective sheet 230, a first optical sheet 240, a second optical sheet 250, and a third optical sheet 260. The LEDs 220 are arranged in the housing 210 at selected intervals. Each LED 220 includes a base portion 222 and a light emitting portion 224. The light emitting portion 224 is made of a plastic material. The first, second and third optical sheets 240, 250 and 260 can be selected from the group consisting of a diffusion panel, a diffusion sheet, and a prism sheet. The first, second and third optical sheets 240, 250 and 260 are arranged above the LEDs 220 in that order. The reflective sheet 230 defines a plurality of through holes (not labeled). The light emitting portions 224 of the LEDs 220 protrude through the corresponding through holes of the reflective sheet 230.
In the above-described backlight module, the reflective sheet 230 is substantially a plastic thin sheet. Thus, a metal sheet 270 is disposed beneath the reflective sheet 230 for supporting the reflective sheet 230. However, the metal sheet 270 increases a weight and a cost of the backlight module. In addition, the metal sheet 270 itself is thin and easily deformed. If the metal sheet 270 is accidentally bent, it is difficult to restore the metal sheet 270 to its original flatness. The deformed metal sheet 270 may displace the light emitting portions 224 of the LEDs 220, and may cause deformation of the reflective sheet 230. Either of these problems is liable to result in a lower efficiency of utilization of light emitted by the light emitting portions 224. Furthermore, in order that the metal sheet 270 can engage with the LEDs 220, a plurality of installation holes are defined in the metal sheet 270. When the metal sheet 270 is assembled in the backlight module, the light emitting portions 224 are liable to be damaged by the metal sheet 270 at the installation holes. This is because the light emitting portions 224 are made of plastic material.
Therefore, a new backlight module is desired in order to overcome the above-described shortcomings.